Impact of dineutrons on nuclear compositions of a core-collapse supernova

TL;DR

This paper investigates how multineutron states $^2n$ and $^4n$ could influence the nuclear composition in the hot, neutron-rich core of a core-collapse supernova. It applies nuclear statistical equilibrium (NSE) with an excluded-volume Boltzmann gas to 3556 nuclei, explicitly including $^2n$ and $^4n$ with Earth-bindings $B(^2n)=-0.066$ MeV and $B(^4n)=0.42$ MeV, using thermodynamic inputs from a two-dimensional axially symmetric SN simulation at 100 ms post-bounce. The results show that $^2n$ and $^4n$ become more abundant than deuterons within roughly 100 km and 50 km, respectively, and their presence reduces the free neutron fraction while increasing protons, deuterons, and $^4$He; the sensitivity study indicates $B(^2n)$ primarily affects its own abundance, while $B(^4n)$ has little impact on the overall composition. The findings imply potential changes to neutrino-matter interactions and neutronization in the SN core and motivate incorporating multineutron states into future EOSs and neutrino-transport calculations, while acknowledging uncertainties in in-medium bindings and the need for more rigorous many-body treatments.

Abstract

We study the nuclear compositions in the central region of a core-collapse supernova, assuming the existence of dineutrons ($^2n$) and tetraneutrons ($^4n$). At 100~ms after core bounce, ${}^2n$ and ${}^4n$ are more abundant than deuterons within radii of approximately 100 and 50~km, respectively. Compared to the model ignoring the existence of ${}^2n$ and ${}^4n$, the mass fraction of neutrons up to a radius of 100~km reduces, while the mass fractions of protons, deuterons, and $\rm{{}^4He}$ increase. Due to the uncertainties in the properties of $^2n$ and $^4n$, we investigate the influence of their binding energies on the nuclear composition. We find the binding energy of $^2n$ has only a modest effect on the overall composition, except for its own mass fraction, while that of $^4n$ has a negligible impact.

Figures (9)

• Figure 1: Mass density distributions at 100 and 200 ms after core bounce on the left and right, respectively. The radius is shown up to 500 km, with scale intervals of 100 km.
• Figure 2: Temperature distributions at 100 and 200 ms after core bounce on the left and right, respectively.
• Figure 3: Electron ratio distributions at 100 and 200 ms after core bounce on the left and right, respectively.
• Figure 4: Mass fraction of the dineutron (left) to the deuteron (right) at 100 ms after core bounce.
• Figure 5: Mass fraction of the dineutron (left) to the deuteron (right) at 200 ms after core bounce.